Process for the preparation of acrylic and methacrylic acids

ABSTRACT

PROCESS FOR THE PREPARATION OF ACRYLIC OR METHACRYLIC ACID, INVOLVING THE VAPOR PHASE OXIDATION OF PROPYLENE OR ISOBUTYLENE, RESPECTIVELY, AT TEMPERATURES OF UP TO 300* C. AND IN THE PRESENCE OF A CATALYST COMPOSITION CONTAINING PHOSPHORIC ACID AND A CATALYTICALLY EFFECTIVE AMOUNT OF PALLADIUM METAL. THE ACRYLIC OR METHACRYLIC ACIDS ARE SELECTIVELY PRODUCED IN THE SIINGLE STEP VAPOR PHASE PROCESS.

U.S. Cl. 260-533 N 8 Claims ABSTRACT OF THE DISCLOSURE Process for thepreparation of acrylic or methacrylic acids, involving the vapor phaseoxidation of propylene or isobutylene, respectively, at temperatures ofup to 300 C. and in the presence of a catalyst composition containingphosphoric acid and a catalytically effective amount of palladium metal.The acrylic or methacrylic acids are selectively produced in the singlestep vapor phase process.

RELATED APPLICATION This application is a continuation-in-part of US.application Ser. No. 99,283, filed Dec. 17, 1970, and now abandoned.

BACKGROUND OF THE INVENTION The present invention relates to a processfor the preparation of acrylic or methacrylic acids by the catalyticoxidation of propylene or isobutylene, respectively, in the vapor phase.

A number of processes have recently been proposed for the vapor phaseoxidation of propylene or isobutylene to form, inter alia, acrylic acidor methacrylic acid. Such processes are described, for example in US.Pats. Nos. 3,065,264; 3,293,290; 3,392,196; 3,401,198; 3,428,674; and3,475,488.

One such process which has been developed and utilized for thepreparation of acrylic acid, for example, involves a multi-stepprocedure for the vapor phase oxidation of propylene into acrolein andacrylic acid. The prescribed multi-step operations present obviousprocessing problems. Moreover, the acrylic acid formed in the successivereaction zones is subject to autoxidation, resulting in relatively lowproduct yields.

It is among the objects of the present invention to provide a new andimproved process for the selective preparation of acrylic andmethacrylic acids in substantial conversions. Other objects andadvantages of the invention will be apparent from consideration of thefollowing detailed description of preferred forms thereof.

SUMMARY OF THE INVENTION In accordance with the present invention,propylene or isobutylene is oxidized in the vapor phase with molecularoxygen at temperatures of up to 300 C. and in the presence of a catalystcomposition containing phosphoric acid and a catalytically effectiveamount of palladium metal, to selectively form the desired acid. Theprocess is carried out at elevated temperatures, employing aheterogeneous catalyst contact system, e.g., a system utilizing a fixed,moving or fluidized catalyst bed. The reactions thus United StatesPatent O 3,792,086 Patented Feb. 12, 1974 carried out, employing theprocess of this invention, may be illustrated by the followingequations:

CH3 CH It has been found that use of the indicated procedure facilitatesthe selective formation of the respective acids in markedly improvedconversions. Moreover, the direct vapor phase process may be utilizedcommercially. Carrying out the reaction in gas phase is a relativelysimple and eflicient operation since no moving parts are required in theprocessing equipment. Product separation is also simplified since thereaction product can be separated from the reaction mixture byazeotropic or extractive distillation or by solvent extraction. Further,gas phase reactions generally permit continuous operation and do notnecessitate the use of expensive, volatile solvents.

The following description of preferred forms of the invention relatesprincipally to the oxidation of propylene to acrylic acid. It will,however, be understood that the process described herein is similarlyapplicable to the vapor phase oxidation of isobutylene to methacrylicacid, as set forth hereinabove, and that such latter embodiment is,therefore, also embraced within the scope of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The propylene or isobutylenereacted in the present process may be fed in pure form or,alternatively, may be impure in the sense that it may contain minoramounts, e.g., up to about 50 mole percent thereof, of a saturatedhydrocarbon vapor such as methane, ethane or propane gas. The oxygenfeed may similarly be pure oxygen gas or, alternatively, anoxygen-containing gas mixture such as air or air enriched with oxygen.In addition to these materials the gaseous feed mixture reacted in theprocess may contain other inert diluents such as carbon dioxide,nitrogen, acetic acid or acrylic acid, as well as other reactivediluents such as acrolein. The gaseous mixture of such reactants iscontacted with a catalyst composition comprising phosphoric acid and acatalytically effective amount of palladium metal, suitably supported ona conventional catalyst carrier such as, for example, silica, alumina,titania, carborundum, carbon, an ion exchange resin, or the like. Silicais preferably utilized as the catalyst carrier in the process hereof, ithaving been found that catalysts deposited on such a support exhibitsuperior stability characteristics.

The support is impregnated or loaded with the phosphoric acid, and thepalladium metal, whether alone or admixed, alloyed, or in solid solutionwith a minor amount of a further metal e.g., another Group VIII metal,or a Group I-B metal such as silver or gold, is deposited thereon. Asindicated below, the catalytically elfective palladium metal and thephosphoric acid may be deposited on or impregnated in the catalystcarrier in any desired sequence, the combined supported catalystcomposition, however formed, being active in the present vapor phaseprocess. The phosphoric acid may also be added continuously to thereaction mixture in the form of an aqueous solution to maintain atrickle liquid phase over the catalyst bed. In this case, the phosphoricacid in the eflluent mixture may be recovered and recycled.

The palladium metal is incorporated in amounts of from about 0.01 topreferably from about 0.1 to 2%, by weight of the total catalystcomposition. On the other hand, the phosphoric acid is incorporated inamounts of at least about 1% and up to as much as about 50%, preferablyfrom about 5 to 30%, by weight of the total catalyst composition.

It has been found, in accordance with the present invention, that othercatalyst compositions, e.g., palladium metal-containing catalystcompositions, which do not incorporate phosphoric acid, or catalystcompositions containing noble metals, other than palladium, either withor without phosphoric acid, e.g., platinum, are not useful in theprocess. Thus, platinum metal cannot be employed as a catalyst in thevapor phase oxidation of propylene since the use of such material as acatalyst results in extensive combustion of the olefin to carbon dioxideand water. Similarly, when it is attempted to utilize palladium chlorideas the catalyst, halogenation of the olefin occurs as well as somedimerization and trimerization thereof. On the other hand, palladiummetal-phosphoric acid catalyst compositions provide the highestconversions to, and selectivities of, acrylic or methacrylic acidproduction.

Palladium metal-phosphoric acid-Group VIII or Group I-B catalystcompositions are similarly active and may exhibit improved stabilitycharacteristics as well.

Deposition of the catalytically effective amount of palladium metalutilized in this process may be effected by conventional techniques,such as by contacting the catalyst support with a solution of a suitablepalladium salt or complex, e.g., palladium chloride, palladium acetate,palladium nitrate or palladium acetylacetonate, and thereafter reducingthe palladium compound to the metal with hydrogen or other appropriatereducing agent. Alternatively, the salt may, if desired, be reacted withalkali to form the corresponding palladium oxide and the latterthereafter reduced to the catalytically active metal.

When the palladium metal is deposited prior to impregnation of thesupport with phosphoric acid the palladium salt may be applied fromeither aqueous or organic media, e.g., water or organic solvent such aslower alkanols, e.g., methanol or ethanol, benzene, chloroform, or thelike. When, on the other hand, the catalytically active palladium metalis deposited on the catalyst support after impregnation of thephosphoric acid, the palladium salt is usually applied from an organicsolvent. Organic media are preferred for deposition of palladium metalin this alternative embodiment inasmuch as the presence of water maytend to remove a portion of the phosphoric acid from the carrier.

The catalyst carrier may be loaded with the phosphoric acid byimpregnating the support with syrupy phosphoric acid, e.g., 85% H PO andsubsequently drying the carrier as, for example, in a vacuum oven. Theimpregnated support may thereafter be calcined to improve bonding of thephosphoric acid to the carrier.

Commercially available catalyst materials may be utilized in thepreparation of the catalyst compositions hereof. Thus, for example,either a commercial supported palladium metal catalyst may be treatedwith phosphoric acid, or a commercial supported phosphoric acid catalystmay have palladium metal deposited thereon, to form catalystcompositions useful herein.

It has been found desirable in accordance with the present invention toadditionally incorporate a protonated material, such as water vapor, inthe reaction mixture. Whether such material acts as a catalyst promoteror otherwise participates in a complex reaction with the olefin is notpresently understood. While such material is, for purposes ofconvenience, referred to hereinafter as a catalyst promoter, it will beunderstood that its use in the vapor phase process is contemplated,irrespective of he actual mechanism by which it may act.

The water vapor may, for example, be added to the gaseous feed mixtureby bubbling the gaseous olefin and/ or oxygen streams through liquidwater. Alternatively, water may be separately vaporized, as by flashing,and metered into the reaction zone. If desired, in lieu of the preferredvapor phase operations of this invention, the water may also be addedcontinuously to the reaction mixture with phosphoric acid to maintain atrickle liquid phase over the catalyst bed.

While stoichiometric proportions of the olefin and oxygen reactants,viz., 1.5 moles of oxygen per mole of propylene or isobutylene, may beutilized in the vapor phase process hereof, such compositions are withinthe flammability range. On the other hand, it may be be prderred tooperate outside flammable ratios and to use reaction mixtures in whicheither the oxygen or the olefin is the limiting reactant. Generally,mixtures are employed in which oxygen is incorporated in amounts of fromabout 5 to 45 mole percent, in admixture with from about 50 to molepercent of the olefin, and, preferably, up to about 60, and desirably 5to 40 mole percent of water vapor promoter. Obviously, when inertdiluents are present in the reaction mixture, e.g., when the oxygen isadded in the form of air, the proportions of the several reactants arecorrespondingly modified. Thus, propylene may be present in amounts ofas low as 5 mole percent when the oxygen is introduced as air. In thecase of trickle phase operation, the molar of water to propylene mayrange between 0.1-10 to 1.0.

The vapor phase reaction is carried out at temperatures markedly lowerthan those which have, heretofore, been generally regarded as necessaryfor vapor phase olefin oxidation reactions. It has previously beenproposed to conduct such reactions at temperatures of the order of about350 to 400 C., at which levels substantial combustion of the olefinreactant occurs.

Surprisingly, however, it has been found that selective formation ofdesired acids may be obtained in accordance with the present inventionat substantially lower temperatures. Thus, the acrylic or methacrylicacids may be obtained at temperatures of as low as 50 to 200 C. orhigher.

The reaction temperature employed in the process varies inversely withthe contact time employed, it being possible to use higher reactiontemperatures when employing shorter contact times and, conversely, lowerreaction temperatures at longer contact times. It has thus been foundpossible to carry out the process of the invention at temperatures of ashigh as 300 C., using relatively short contact times. 1

The oxidation process is conducted either at atmospheric or elevatedpressures, the use of higher pressures somewhat increasing productconversions. The reaction may thus be effected at pressures of up toabout 300 p.s.i. It is, however, generally preferred to carry out thevapor phase process under pressures only slightly in excess ofatmospheric, e.g., up to about 75 p.s.i., to increase productivity andcatalyst efficiency.

After the gaseous reaction mixture contacts the catalyst composition,the exhaust gases are cooled and scrubbed to facilitate recovery of theacrylic or methacrylic acid. The desired material may then be separatedby any convenient means such as distillation. Unreacted feed materialseparated from the recovered efiluent mixture may thereafter berecovered and recycled for further reaction.

The following examples are directed to preferred embodiments of thevapor phase process hereof. In the examples, which are intended asillustrative and which should not be construed in a limiting sense, allparts and percentages are given by weight and temperatures in degreesCentigrade unless otherwise specified. As employed herein, theconversions to acrylic or methacrylic acid,

and the selectivities of formation of such products, are defined asfollows:

Percent conversion Number of Moles of Product Actually Formed Number ofMoles of Product Theoretically Possible Based on Limiting ReactantNumber of Moles of Product Number Moles of Olefin Feed Actually ReactedEXAMPLE 1 Preparation of acrylic acid, employing a 2% palladium- 9.1%phosphoric acid catalyst composition A Pyrex glass reactor 12 x 2.5 cm.(outside diameter), provided with a thermowell (0.8 cm. O.D.), extendingthe entire length of the reactor is attached to a pre-heating zone (1.2x 15 cm.) and a capillary exit tube (0.1 x 10 cm.) to permit rapidquenching. The catalyst composition is prepared by treating grams of 2%palladium supported on alumina with 2.5 grams of phosphoric aciddissolved in 10 ml. of water, followed by heating in an open, rotatingevaporating dish with a heat gun, delivering hot air at 125 C. to removeunbound water. The catalyst is cooled to room temperature, packed in thereactor and heated at 130 C.

A stream of millimoles/hr. (mmoles/hr.) propylene and 23 mmoles/hr.oxygen is passed through the heated catalyst bed. The exhaust reactiongases are passed through a trap maintained at C. Analysis by gaschromatography after 2 hours operation indicates the formation of 3.2mmoles/hr. acrylic acid, with the coproduction of 0.6 mmoles/hr.acrolein, 0.5 mmoles/hr. isopropanol, 0.2 mmoles/hr. allyl acetate and1.13 mmoles/ hr. of propylene are converted to carbon dioxide. Theconversion to acrylic acid is 20.8% and the selectivity of acrylic acidformation is 55% CONTROL A Reaction of propylene and oxygen, employingpalladium only as the catalyst composition Percent selectivity= X 100For purposes of comparison, the procedure described in the precedingexample is repeated employing, however, as the catalyst composition alike quantity of 2% palladium metal on alumina catalyst compositionwhich has not been impregnated with phosphoric acid. After 23 hoursoperation analysis of the eflluent mixture indicates the formation of0.1 mmole/hr. acrylic acid (a conversion of only 0.63%), and theco-production of trace amounts of acetic and propionic acids, acetone,acrolein allyl acetate and allyl acrylate. The selectivity to acrylicacid is only 5.1%.

EXAMPLE 2 Preparation of acrylic acid, employing a 2% palladium- 11%phosphoric acid catalyst composition The procedure described in Example1 is repeated employing 28.1 grams of a 2% palladium-11% phosphoric acidon alumina catalyst composition and feeding an identical gaseous feedmixture thereover. Analysis of the effiuent mixture indicates theformation of 5.46 mmoles/ hr. acrylic acid, and the co-production of0.55 mmole/hr. acrolein, 0.6 mmole/ hr. isopropanol, 0.15 mmole/ hr.allyl acetate, 1.2 mmole/hr. acetone and a trace amount 6 of aceticacid. The conversion to acrylic acid is 35.6% and the selectivity ofacrylic acid formation is 63%.

CONTROL B Reaction of propylene and oxygen, employing palladium only asthe catalyst composition For purposes of comparison, the proceduredescribed in Example 2 is repeated employing, however, as the catalystcomposition 25 grams of a 2% palladium metal on alumina which has notbeen impregnated with phosphoric acid. After 24 hours operation,analysis of the eflluent mixture indicates the formation of 0.11mmole/hr. acrylic acid (a conversion of only 0.6%) and the co-productionof 5.98 mmoles/hr. carbon dioxide as well as trace amounts of acetone.

EXAMPLE 3 Preparation of acrylic acid, employing a 1.3% palladium 0.55%gold-9.0% phosphoric acid catalyst composition The procedure describedin Example 1 is repeated, employing 27.5 grams of a 1.3% palladium,0.55% gold and 9.1% phosphoric acid on alumina catalyst composition andfeeding a gaseous feed mixture containing 35 mmoles/hr. propylene and 23mmoles/hr. oxygen thereover. Analysis of the efliuent mixture indicatesthe for mation of 5.81 mmoles/hr. acrylic acid and the co-production of0.2 mmole/hr. acrolein, 0.6 mmole/hr. isopropanol, 0.1 mmole/hr. allylacetate, 0.8 mmole/hr. acetone, and a trace amount of acetic acid. Theconversion to acrylic acid is 38.0% and the selectivity of acrylic acidformation is 67.0%.

EXAMPLE 4 Preparation of acrylic acid, employing a 1.3% palladium 0.55%gold-11.09% phosphoric acid catalyst composition The procedure describedin Example 3 is repeated, em-

ploying 25 grams of a 1.3% palladium, 0.55% gold and 11% phosphoric acidon alumina catalyst composition and feeding a gaseous feed mixturecontaining 35 mmoles/hr. propylene and 23 mmoles/hr. oxygen thereover.Analysis of the effluent mixture indicates the formation of 6.31mmoles/hr. acrylic acid and the co-pro duction of 0.4 mmole/hr.acrolein, 0:6 mmole/hr. isopropanol, 0.1 mmole/hr. allyl acetate, 1.2mmoles/hr. acetone, and 1.17 mmoles/hr. of propylene are converted tocarbon dioxide. The conversion to acrylic acid is 41.2% and theselectivity of acrylic acid formation is 64%.

EXAMPLE 5 Preparation of acrylic acid, employing a 1.3% palladium- 0.55%gold-11.0% phosphoric acid catalyst composition and water vapor as apromoter The procedure described in Example 4 is repeated, employing alike quantity of a 1.3% palladium, 0.55% gold, and 11.0% phosphoric acidon alumina catalyst composition. A gaseous feed of 35 mmoles/hr.propylene and 23 mmoles/hr. oxygen is bubbled through water heated at 70C. at 1 atmosphere. The mixed vapors are then fed into the heatedcatalyst composition at C. Analysis of the efiluent mixture indicatesthe formation of 4.21 mmoles/hr. acrylic acid and the co-production of0.6 mmole/hr. acrolein, 1.0 mmole/hr. isopropanol, a trace amount ofacetic acid and no acetone or allyl acetate. The conversion to acrylicacid is 27.5% and the selectivity of acrylic acid formation is 63%.

EXAMPLE 6 v Preparation of acrylic acid, employing a 2% palladium-9.10-% phosphoric acid composition and water vapor as a promoter Theprocedure described in Example 5 is repeated employing 27.5% grams of a2% palladium-9.1% phosphoric acid on alumina catalyst and feeding anidentical gaseous feed mixture. Analysis of the efiluent mixtureindicates the formation of 3.67 mmoles/ hr. acrylic acid and theco-production of 0.5 mmole/hr. acrolein, 0.4 mmole/ hr. isopropanol andtraces of allyl acetate and acetic acid. The conversion to acrylic acidis 24.0% and the selectivity of acrylic acid formation is 65%.

CONTROL C Reaction of propylene and oxygen, employing palladium only asthe catalyst composition For purposes of comparison, the proceduredescribed in Example 6 is repeated employing, however, a like quantityof a 2% palladium metal on alumina catalyst composition which has notbeen impregnated with phosphoric acid. After six hours operationanalysis of the effluent mixture indicates the formation of 1.0mmole/hr. acrylic acid (a conversion of only 6.5%) and the co-productionof 0.2 mmole/hr. acrolein.

EXAMPLE 7 Preparation of acrylic acid, employing apalladiumsilver-phosphoric acid catalyst composition The procedure ofExample 1 is repeated employing 26.1 grams of 2.0% palladium, 0.2%silver and 11.2% phosphoric acid as the catalyst.

Analysis of the reaction mixture, after two hours of operating time,discloses the presence therein of 2.4% acrylic acid, 0.4% acrolein, 1.0%acetone, 0.6% isopropyl alcohol and 0.15% allyl acetate. The conversionto acrylic acid is 15.6% based on the oxygen feed per pass, with 51%selectivity based on the propylene converted to volatile products(including carbon dioxide).

EXAMPLE 8 Preparation of methacrylic acid, employing a 1.8%palladium-11.0% phosphoric acid catalyst composition The procedure ofExample 1 is repeated employing 28 grams of a catalyst compositioncontaining 1.8% palladium and 11.0% phosphoric acid supported on aluminaand using isobutylene instead of propylene. The gaseous feed streamconsists of 34.5 mmoles/hr. of isobutylene and 23 mmoles/hr. of oxygen.The reaction mixture is passed through a trap held at C.

After two hours of operation time, the condensate is analyzed by vaporphase chromatography and mass spectra. The analysis shows formation ofmethacrylic acid at the rate of 0.5 mmole/hr. corresponding to aconversion of 3.3% based on the oxygen feed per pass.

EXAMPLE 9 Preparation of acrylic acid, employing a 2%palladiumphosphoric acid on silica catalyst composition Example 1 isrepeated except the catalyst comprises a 2% palladium-25% phosphoricacid catalyst on a silica gel carrier. The catalyst is packed in thereactor (described in Example 1) and heated at 170 C. A stream ofpropylene and air containing 67.4 mmoles/hr. oxygen and 95.0 mmoles/hr.propylene is bubbled through water heated at 80 C. The mixed vapors arepassed through the heated catalyst.

Analysis of the condensate shows formation of acrylic acid at the rateof 16.2 mmoles/hr. The conversion to acrylic acid is 36.1% based on theoxygen feed with a selectivity of 81.2% based on the propylene convertedto volatile products.

EXAMPLE 10 Preparation of acrylic acid, employing a 2%palladiumphosphoric acid on alumina catalyst composition Example 9 isrepeated except the catalyst is 2% palladium on an alumina carrier with30% phosphoric acid heated at 150 C., and the feed of propylene and aircontains 48 mmoles/hr. oxygen and 67 mmoles/hr. propylene. Analysis ofthe condensate shows formation of acrylic acid at the rate of 15mmoles/hr. The conversion to acrylic acid is 50.4% based on the oxygenfeed with a selectivity of 83.6%, based on the propylene converted tovolatile products.

The conversion and selectivity data obtained in the precedingexperiments is tabulated below:

TABLE I [Calculated conversions and 50.186121107181505 in Examples 1-10and Controls Percent convcr- Percent sion per sch-c- Catalystcomposition 1 pass 2 tivity Example 1.-.. 2% Pd, 9.1% HBPOA-.. ControlA.... 2 0 Example 2.... 2% Pd, 11.0% HaPO Control B 2% Pd Example 3....1.3% Pd, 0.55% Au, 0.1% H3P04.. Example 4.... 1.3% Pd, 0.55% Au, 11.0% HPO4.-..

Example 5.-.. 1.3% Pd, 0.55% Au,11.0% H3PO4...- Example 6.-.. 2% Pd,9.1% H3PO4 Control C 2% Pd Example 7. 2% Pd, 0.2% Ag, 11.0% HSPO Example8. 1.8% 3PO4 Example 9.-.- 2% Pd 25 3PO4 Example 10... 2% Pd, 30% H3PO41 Water vapor is used as a promoter in the experiments of Examples 5 and6. Aluminais used as the support for each of the catalyst compositionsemployed, with the exception of the composition utilized in Example 9,for which silica is used as the catalyst carrier.

2 In all examples other than Example 8, the conversions andselectivities are given in terms of the production of acrylic acid,based upon the limiting reactant in the respective experiments. InExample 8, the tclonversion is given with reference to the production ofmethacrylic acid ierem.

EXAMPLES 1l-17 Preparation of acrylic acid, employing miscellaneouspalladium on silica catalyst compositions The catalysts identified inTable II below are prepared by simultaneous deposition of theappropriate metal chloride or mixed metal chlorides from aqueoussolution on extruded silica, followed by reduction with gaseous hydrogenat 200 C. The catalysts are thereafter loaded with 25% H PO (based ontotal catalyst weight). The volume.

TABLE II [Conversions and seleetivities in Examples 11-17] Catalystcomposition Percent eon- Percent selecversion tivity to Example Pd 1Co-metal l per pass acrylic acid 2 1 Weight percent of metal based ontotal catalyst weight.

2 The major by-products are acrolein and carbon dioxide with minoramounts of propionic acid, acetic acid and isopropanol.

The present invention thus provides an improved process for theproduction of acrylic and methacrylic acids by the vapor phase oxidationof propylene and isobutylene, respectively. Since various modificationsmay be made in the preferred embodiments of the process describedhereinabove, the scope of the invention should rather be determined fromthe claims appended hereto.

We claim:

1. A process for the preparation of acrylic or methacrylic acid, whichcomprises oxidizing propylene or isobutylene, respectively, withmolecular oxygen in the vapor phase, in the presence of a catalyticallyeffective amount of a catalyst consisting essentially of a palladiummetal, and in the presence of a Group VIII or a Group I-B metal, saidmetals being supported on a carrier impregnated with phosphoric acid,the palladium metal being present in an amount of from 0.01 to by weightof the total catalyst composition, and the phosphoric acid being presentin an amount of at least 1% by weight of the total catalyst composition.

2. The process of claim 1, wherein the oxidation is carried out in thepresence of gold metal as the Group I-B metal.

3. A process for the preparation of acrylic or methacrylic acid, whichcomprises oxidizing propylene or isobutylene, respectively, withmolecular oxygen in the vapor phase and in the presence of acatalytically eifective amount of a catalyst consisting essentially ofpalladium metal, said palladium metal being supported on a carrierimpregnated with phosphoric acid, the palladium metal being present inan amount of from 0.01 to 5% by Weight of the total catalystcomposition, and the phosphoric acid being present in an amount of atleast 1% by Weight of the total catalyst composition.

4. The process of claim 3, wherein the reaction is carried out attemperatures of up to 300 C. and under pressures of up to 300 p.s.i.

5, The process of claim 3, wherein the respective materials are reactedin proportions of from 5 to 95 mole percent of propylene or isobutylenewith from 5 to mole percent oxygen.

6. The process of claim 5, wherein the gaseous reaction mixture furtherincludes Water vapor in an amount of up to 45 mole percent thereof.

7. The process of claim 3, in which propylene is oxidized to produceacrylic acid.

8. The process of claim 3, in which isobutylene is oxidized-to producemethacrylic acid.

References Cited UNITED STATES PATENTS 3,624,147 11/1971 David et al260-533 N FOREIGN PATENTS 971,666 9/ 1964 United Kingdom 260533 NLORRAINE A. WEINBERGER, Primary Examiner R. D. KELLY, Assistant ExaminerU.S. Cl. X.R.

252--430, 437; 260-497 A, 597 B, 604 R, 632

